LITTLE ROCK (AP) — Three siblings in Arkansas have been diagnosed with suspected measles and a Benton County boarding school that two of the children attend has sent home all children who haven't been immunized, the state Health Department said Tuesday.

The agency said the children — ages 10, 14 and 17 — had not been immunized. Two of them attend Ozark Adventist Academy, a residential high school near Gentry, which has sent home an undisclosed number of students who hadn't been immunized, the agency said.

Dr. Gary Wheeler, branch chief for infectious diseases for the Arkansas Health Department, said the agency is waiting for lab tests to confirm the cases but sent out an alert after the children presented symptoms of the virus.

Small measles outbreaks have been popping up in the U.S., usually after international travel. One of the children had recently returned from visiting Romania, Italy and Switzerland. That child became ill and the youth's two siblings developed symptoms while at the high school.

"There are still little pockets of (measles cases) that spring up in surprising places like Switzerland, which obviously is a very modern place," Wheeler said. "Most of that is related to the low immunization rates."

Arkansas is among states that allow parents to declare a "philosophical" objection to having their children immunized. The number of exemptions has grown from a few hundred in 2003 to more than 3,600 last year, though that is still less than 1 percent of the state's 468,000 public school students.

Wheeler said measles is spread "at least as easily as a cold" and the way to prevent outbreaks is to have a very high number of people immunized.

The vaccine is ineffective for a small percentage of people. People with compromised immune symptoms, such as people undergoing chemotherapy and HIV patients, are also vulnerable to the disease. So are infants who are less than a year old and too young for the shots.

The virus causes fever, runny nose, cough and a distinctive red-spotted rash all over the body. Complications can include pneumonia, encephalitis and, later in life, progressive neurologic symptoms that Wheeler said can be debilitating. The illness can be fatal.

Wheeler said health agencies should drive home the point that being immunized is a community service.

"I think we need to support people who do get their immunizations. They're contributing to the public health of everybody," he said.

Wheeler said measles outbreaks are a challenge for health professionals because they are often associated with travel. The disease is contagious before symptoms start to show.

"It is sort of a public health nightmare to track down all those people who were on the airplane and make sure they are all immunized," he said.

Wheeler wouldn't address what steps were being taken with the Arkansas cases. In general, he said, health officials scramble to find anyone who may have been exposed and find out if they've been immunized.

The website for Ozark Adventist Academy advises families that the school is following Health Department guidelines in sending home students who weren't up to date on their shots.